My husband and I have rented two homes together and are on our second home that we have bought. One thing that never fails to amaze us is how odd the wiring in any given house can be...especially in our current house.
We have a light switch that cuts power to the dishwasher. If my husband is using any power tool on the original outlet in the garage and I decide to blow dry my hair, we will trip a circuit and lose power to my master bath, the garage and half of the kitchen. (the kitchen is on the opposite side of the house of the master bath and garage)
After that experience and many other odd ones, we decided we needed to map the electrical in our house. This has not only saved us a lot of time, but money. Anytime we have an electrician out, they no longer need to figure it out all by themselves and charging us $60-100 per hour to do so. We bought a circuit tester, we had our cell phones, and a rough sketch of our house. I stood out by the electrical panel outside and started by labeling every circuit breaker A-J. Hubby and I were on our phones talking with each other and I would flip one switch and hubby would tell me what it controlled. We did this until EVERYTHING had a label. It took over an hour, but we now rely on it heavily.
To prove my point of how needed this is. The switch that controls the overhead light in the garage blew out this week. So, I pulled out my electrical map and looked for the garage light which is on circuit D. When my hubby goes to replace the switch, he knows he needs to shut off that circuit and he won't get shocked. (We ALWAYS double check, just to be safe).
We now plan to do this in any house we buy from here on out. It's too useful and money saving not to do it.
Below is the circuit tester we use. You can pick it up/or one similar at any hardware store. It beeps and lights up if there is power to the circuit, it does nothing if no power is present.
I have shared this over at the Trick or Tip link party happening at Sawdust and Paperscraps.